This paper presents Olan, a language and a run time support intended to facilitate the design, configuration and evolution of distributed applications made up of heterogeneous software components. Configuration covers two phases: for the application builder, the identification of the software components and the description of their interconnections and communications; for the application administrator, the accurate use of system resources provided by the target environment; for the deployment of the application on the target environment. The main benefit of Olan is to provide a single unified description of distributed applications, adequate for construction, management, and evolution. The overall description is independent from the components' implementation, so that the configuration process, e.g. the production of different versions of an implementation, is decoupled from the programming process.